Compiler warning (level 1) C4930 error

Environment:

Win7 32bits

Visual Studio 2013

Reference: Https://msdn.microsoft.com/zh-cn/library/4ddd21xh.aspx

Error Description "Prototype": the prototype function is not invoked (is it intentionally defined with a variable? )

The following example produces a C4930 error

c4930.cpp//compile with:/w1class Lock {public:   int i;}; void F () {   Lock thelock ();   C4930   //try the following line instead   //Lock Thelock;} int main () {}

C4930 also occurs when the compiler cannot distinguish between function prototype declarations and function calls.

c4930b.cpp//compile with:/ehsc/w1class booleanexception{bool _result;public:booleanexception (bool result)   : _result (Result) {} bool GetResult () const {return _result; }};template<class T = Booleanexception>class Iffailedthrow{public:iffailedthrow (bool result) {if (!result      ) {throw T (result);         }}};class Myclass{public:bool MyFunc () {try {iffailedthrow<> (MyMethod ());//C4930         Try one of the following lines instead//iffailedthrow<> IFT (MyMethod ());         Iffailedthrow<> (This->mymethod ()); Iffailedthrow<> ((*this).         MyMethod ());      return true;      } catch (Booleanexception e) {return e.getresult ();   }}private:bool MyMethod () {return true;   }};int Main () {MyClass MyClass; Myclass.myfunc ();}

in the example above, the result of a method without parameters is passed as a parameter to the constructor of the unnamed local class variable. The call is ambiguous: it can be either a named local variable or a method call prefixed with the object instance and the corresponding pointer operator to the member.

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In my own code, C4930 errors occur in the following situations:

Class Mycomparison{bool Reverse;public:mycomparison () {//cout << "construct" << Endl;} Mycomparison (bool revparam) {reverse = Revparam;} BOOL Operator () (const int& LHS, const INT&RHS) Const{return LHS > rhs;//if (reverse) return (LHS>RHS);//els e return (LHS<RHS);};

declare the priority queue in the main function:

int main () {priority_queue<int, vector<int>, Mycomparison>pq (Mycomparison ());//c4930system ("pause"); return 0;}

I thought I created a temporary variable, and the compiler could understand it as a function declaration, the return value is Priority_queue, the function name is PQ, and the parameter is a pointer to the functions that omit the specific return type.

There are two types of modifications that can be made:

The first way:

Priority_queue<int, Vector<int>, Mycomparison>pq ((Mycomparison ()));//Supplementary brackets

The second way:

Priority_queue<int, Vector<int>, Mycomparison>pq (Mycomparison::mycomparison ());//Add:: Access symbol

Reference: http://stackoverflow.com/questions/12041509/possible-compiler-bug-for-c4930

Compiler warning (level 1) C4930 error